When trying to access phabricator via https://p.phcdn.net people are presented with an exception.
Message: "This Phabricator install is configured as "https://secure.phabricator.com/", but you are using the domain name "p.phcdn.net" to access a page which is trying to set a cookie. Acccess Phabricator on the configured primary domain or a configured alternate domain. Phabricator will not set cookies on other domains for security reasons."
This is intentional, and the expected behavior.
Why are you trying to access p.phcdn.net? What did you expect to happen?
Compare to Google's similar user content domain:
I thought it may be intentional, but I would not consider it 'proper'. (see note on google, below)
tbh. I had a tab open for the past month or so and for reason unknown to me it was at that address. I don't remember how I got there in the first place, but I doubt I purposefully entered it into address bar.
A note on the google user content: Google sends 404, whereas Phabricator sends 500 with an exception message
If there's some way to arrive here without purposefully following a link to it or entering it into the address bar, we'll fix that. Short of that, this is behaving as intended.